The present invention relates to magnetic memory systems, and more particularly to a method and system for providing tunneling magnetoresistive sensors that could be used in magnetic memory systems.
Magnetic memories are often used in storing data. One type of memory currently of interest utilizes tunneling magnetoresistive (xe2x80x9cTMRxe2x80x9d) sensors in the memory cells. A TMR sensor typically includes two ferromagnetic layers separated by a thin insulating layer. The insulating layer is thin enough to allow charge carriers to tunnel between the ferromagnetic layers. One ferromagnetic layer has its magnetization fixed, or pinned, in place. This is typically accomplished using an antiferromagnetic layer. The other ferromagnetic layer has a magnetization that can rotate in response to an applied magnetic field. The resistance of the TMR sensor depends upon the orientation of the magnetic tunneling junctions. Thus in order to store data in the TMR sensor or MRAM, one or two magnetic fields are applied to rotate the magnetization of one of the layers. Typically, the magnetization of one ferromagnetic layer will be rotated to be parallel or anti-parallel relative to the magnetization of the other ferromagnetic layer. The TMR sensor will thus be in either a low resistance (magnetizations parallel) or a high resistance (magnetizations antiparallel) state. The TMR sensor can thus be used to store data. A signal corresponding to the resistance is developed in order to indicate the type of data stored.
FIG. 1 is a flow chart depicting a conventional method 10 for fabricating the TMR sensor. FIGS. 2A-2E depict a conventional TMR sensor during fabrication. Referring to FIGS. 1 and 2A-2E, the method 10 commences after the layers for the TMR sensor have been deposited. Thus, the method 10 starts after the free layer, the tunneling barrier and the pinned layer and antiferromagnetic layer which pins the magnetization of the pinned layer, have been provided on a bottom lead layer. A conventional bilayer structure is provided, via step 12. FIG. 2A depicts the conventional TMR structure 50 after step 12 has been performed. The TMR layers 54 reside on a bottom lead 52. The TMR layers include an antiferromagnetic layer, a ferromagnetic pinned layer, a tunneling barrier (a thin insulating layer) and a ferromagnetic free layer. Also depicted is the conventional bilayer structure 56 that includes a PMGI layer 55 and a larger photoresist layer 57.
Using the conventional bilayer structure 56 as a mask, the TMR sensor is defined, via step 14. FIG. 2B depicts the conventional TMR structure 50 after the conventional TMR sensor 60 has been defined. A dielectric layer is provided, via step 16. FIG. 2C depicts the TMR structure 50 after the dielectric layer has been deposited. The dielectric layer includes regions 62A and 62B on either side of the conventional TMR sensor 60 as well as a region 62C that lies on the conventional bilayer structure 56. The conventional bilayer structure 56 is lifted off, via step 18. FIG. 2D depicts the conventional TMR structure 50 after the conventional bilayer structure 56 has been removed. A top lead is provided, via step 20. FIG. 2E depicts the conventional TMR structure 50 after the top lead 64 has been provided.
Although the conventional method 10 provide the conventional TMR sensor 60, one of ordinary skill in the art will readily recognize that the conventional bilayer structure 56 may limit the size of the TMR sensor that can be provided. The bilayer photoresist structure 56 requires an undercut of approximately 0.05 xcexcm on each edge. The undercut is utilized to ensure that the conventional bilayer structure 56 can be lifted off. For smaller TMR sensors, the conventional bilayer structure 56 may easily be inadvertently removed before steps 16 and 18 are completed. This is particularly true for TMR sensors 60 which have aminimum dimension of 0.2 xcexcm in length or less. Thus, it becomes difficult to fabricate smaller devices having a minimum dimension of approximately 0.2 xcexcm or less. For such devices, the yield decreases. In addition, electrostatic discharge damage and particle contamination also become an issue for device made using the conventional method 10. Consequently, it is difficult to fabricate smaller TMR sensor 60.
Accordingly, what is needed is a system and method for providing a shorter TMR sensor. The present invention addresses such a need.
A method and system for providing a tunneling magnetoresistive sensor is disclosed. The method and system include providing a pinned layer, a free layer and an insulating layer between the pinned and free layers. The pinned and free layers are ferromagnetic. The method and system also include providing a hard mask layer to be used in defining the sensor at the top of the tunneling magnetoresistive sensor. The method and system also include using the hard mask layer to define the tunneling magnetoresistive sensor. Thus, the pinned layer, the free layer and the insulating layer are capable of being less than 0.2 xcexcm in length.
According to the system and method disclosed herein, the present invention provides a smaller tunneling magnetoresistive sensor.